# 已在navicat中运行正常
# 练习常用的运算符 ：
# SELECT 5 div 3 取商
# SELECT 5 + 3
# SELECT 5 - 3
# SELECT 5 mod 3 取余
# 比较运算符：
# SELECT 1 =1
# SELECT 1 <=1
# SELECT 2 not between 1 and 3
# SELECT 4 is not null
# 函数：
# SELECT sum(quantity) from class2
# SELECT avg(quantity) from class2
# SELECT count(quantity) from class2
# 字符处理
# SELECT CHAR_LENGTH("test123")
# SELECT FORMAT(0.2222,2)
# SELECT right("abcdefgggg", 2)
# SELECT trim("abcdefg        ")
